1. Field of the Invention
The present invention relates to a system for levitating and guiding an object by magnetic force, typical examples of which are a superconducting magnetic supporting apparatus and a superconducting linear convey system.
2. Description of the Related Art
In a convey apparatus used in a super-clean space of, e.g. a clean room, it is desired that no dust occurs during a convey operation. Accordingly, as regards the convey apparatus used in such an atmosphere, it is desired that a convey vehicle be run in a perfect non-contact state. In order to run the convey vehicle in the perfect non-contact state, it is necessary that the convey vehicle be levitated along a convey path by some means and a propelling force be applied to the convey vehicle in a perfect non-contact state.
There are several methods for levitating the convey vehicle along the convey path. In a generally employed system, the convey vehicle is levitated by magnetic force. There are two systems for levitating the convey vehicle by magnetic force: one requiring high-level control, and the other requiring no control. The latter contributes to simplification in design, manufacture and maintenance of the convey apparatus.
For example, Published Unexamined Japanese Patent Application (PUJPA) No. 1-133840 discloses a convey apparatus wherein means for magnetically levitating a convey vehicle with no control is achieved. In the convey apparatus disclosed in this document, a superconductor which comes into the superconducting state at a temperature equal to or higher than a liquid nitrogen temperature is mounted on a convey vehicle. The convey vehicle is levitated by making use of the Meissner effect caused by the superconductor in the superconducting state. Specifically, in this convey apparatus, the convey vehicle is levitated by a magnetic repulsion force created between the superconductor mounted on the convey vehicle and a magnetic field generating device provided on the convey path side. In this convey apparatus, a train of coils is provided on the convey path side. The superconductor is magnetically trapped between magnetic poles produced by exciting each coil of the coil train. By sequentially switching excitation of each coil, the trapping position is shifted. Thereby, a propelling force is applied to the convey vehicle.
However, in the above convey apparatus, since the convey vehicle is levitated and guided by making use of the Meissner effect of the superconductor, it is difficult to obtain a guide force enough to run the convey vehicle along the convey path. Consequently, when an external force such as a centrifugal force is applied to the convey vehicle, the convey vehicle tends to be derailed from the convey path and a problem remains with respect to the stability of running.
When the width of the superconductor is greater than the width of the levitation magnetic field applied from the convey path side, the magnetic guide force cannot be applied to the convey vehicle. Thus, the degree of freedom of design of the convey vehicle is low.
Furthermore, when the center of gravity of the convey vehicle deviates due to the weight of a load, etc., it is difficult to keep the desirable levitation state.
As has been described above, in the prior art, the convey vehicle is levitated and guided by making use of the Meissner effect of the superconductor, the degree of freedom of design of the convey vehicle is low. Moreover, when the center of gravity of the convey vehicle deviates due to the weight of a load, etc., it is difficult to keep the desirable levitation state.